There are 37 lakes in the Qaidam Basin: 1 freshwater lake

6 brackish-water lakes

2 saline-water lakes and 28 salt lakes. The pH value of salt lake brines is 7.014 on the average

and the average total mineralization is 340.75 g/1. Their water bodies belong mainly to the five-component equilibrium system

: Na

K

Mg//SO4

Cl-H2O

which can be further grouped into sodium-magnesium sulfate subtype

magnesium sulfate subtype

chloride transition subtype and chloride type water by their hydrochemical property. The salt lake brines of the first salt forming epoch (N2−Q3) were of the sulfate type. In the second salt forming epoch (Q3−Q4)

some of them were of the chloride type. The pH value of brines decreases with the increase of total mineralization. The pH value is lower when the total mineralization is from 50–310 g/l and higher when the total mineralization is from 310–355 g/l

however

when the total mineralization is higher than 355 g/l

the pH value decreases slowly again. The total mineralization of the chloride type and the chloride transition subtype brine is higher than the sulfate type

being 310–530 g/l

310–470 g/l

and less than 355 g/l in that order. Of the 40 chemical compositions in the saline lake brines in Qaidam Basin

potassium is mainly concentrated in the chloride type and chloride transition subtype brine

boron and lithium mainly in the sulfate type. Evaporation experiments show that boron and lithium are accumulated in concentrated brine until crystallization of bischofite takes place. Potassium is also accumulated in concentrated brine during the salt forming stage

but its concentration decreases with the increase of total mineralization during the potassium forming stage.